1. Field
The present invention relates to loud speaker enclosures and, in particular, to those containing internal damping systems.
2. Prior Art
A typical prior art speaker enclosure is shown in FIG. 1. FIG. 1A illustrates the front elevation view of the prior art speaker comprising an enclosure 101 and a speaker port 102. FIG. 1B illustrates an internal side view of the speaker enclosure shown in FIG. 1A, comprising the enclosure 101, a speaker 106, and internal sound absorptive padding 103.
The speaker is mounted on the front side panel 108 and positioned to direct the sound outward of the port 102. Padding 103 is distributed about the top 109, bottom 110 and back of the internal walls of the enclosure 101.
In the operation of the enclosure, the speaker 106 produces forward and rearward projected waves. The rearward projected waves, which are indicated by directional arrows 104, strike the rear of the cabinet 107 and are reflected back toward the front of the cabinet 108, as indicated by directional arrows 105. Such waves can continue to reflect back and forth between the walls to produce standing waves which degrade the quality of the reproduced sound. Typically, padding 103 must be added to damp these waves; however, the padding tends to reduce the total sound output which can be obtained from the system.
In some prior art speaker designs, tuning was provided by a passive speaker cone mounted in one of the side panels in a manner similar to speaker 106 shown in FIG. 1B. The cone is not driven by the usual magnetic coils, but is simply a baffle free to float and absorb waves impinging upon it. In some instances, the cone is weighted to provide tuning. Unfortunately, when strong, low frequency sounds such as subsonic sounds, impinge upon the speaker, they drive the cone to a bottoming or limit position which tends to loosen the weight and tear the cone. The active speaker can also be damaged in this design when powerful subsonic frequencies pass through the system by hitting the voice coil against the magnet or through tortional stress.